Continuation of experiments to determine the effects of whole-body mechanical vibration in the range 2 to 32 Hz for exposure durations in the range 16 minutes to 8 hours upon human performance, psychophysiological, and subjective responses. This work is aimed specifically at the appraisement of the current International Standard ISO 2631-1974, "Guide for the Evaluation of Human Exposure to Whole-Body Vibration", which sets limits of vibration acceleration as functions of time and frequency, according to criteria of comfort, human performance, and safety. Qualified human volunteers are exposed to levels of vibration determined by the "Fatigue-Decreased Proficiency Boundary" for various frequencies and exposure durations specified in the Standard. Responses measured include compensatory tracking ability (primary task) and performance of visual and auditory secondary tasks, as well as a number of tests of postural and tactile sensory function, and visual resolution acuity.